As McCain fights brain cancer, Republicans will vote without their 'consummate dealmaker'

A devastating diagnosis that might sideline a key Republican legislator indefinitely isn't just complicating plans to advance U.S. President Donald Trump's agenda, political analysts say. It's also sidelining one of the few influential Republican critics of the administration.

Doctors revealed this week Arizona Sen. John McCain is battling brain cancer, depriving Republican lawmakers of a crucial Senate vote.

Without him, Republicans may not have the numbers to pass legislation to repeal the Affordable Care Act, as well as secure enough support for tax reform, raising the debt ceiling and a $1-trillion infrastructure spending package.

"Every day John McCain is not there is a problem for manoeuvring a Republican agenda through Congress," said Arizona Republican strategist Nathan Sproul. "He's the consummate dealmaker."

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"With just 51 [Republican] votes, that's going to make it even more difficult for majority leader Mitch McConnell to hold things together."

Democrats are expected to vote as a bloc against a bill to repeal and replace the Affordable Care Act next week. Under an expedited procedure known as reconciliation, a simple majority of 51 votes is needed.

Other measures, such as a national defence spending bill, would require an even higher threshold of 60 votes in order to invoke "cloture," shutting off debate to proceed to a vote. Overcoming the filibuster could now become an even bigger challenge.

McCain, 80, is known for his independent-mindedness. He has emerged as a rare voice of Republican dissent against the president's foreign policy, a media favourite who has often criticized the president's actions and stance on Russia.

Jaime Molera, a Republican strategist in Phoenix, noted that the 34-year senator has been strongly aligned with the Republican agenda. A statistical breakdown of his voting record on FiveThirtyEight showed McCain voting in line with the president's proposals 90.5 per cent of the time.

As a lion of the U.S. Senate, Molera said, "his strength comes from being supported by both sides of the aisle and within the various factions of the Republican caucus."

Thomas Volgy, the former Democratic Mayor of Tucson, Ariz., said McCain's stature as a leader in the Senate was built upon his willingness to buck the Republican line when he felt it was right.

"There are very few legitimate outspoken critics in the administration on the Republican side of the Senate," Volgy said.

"John McCain is one of them. And when his voice isn't there, you lose something very important in terms of democratic politics."

McCain and South Carolina Sen. Lindsey Graham often worked in tandem on trying to hold the administration accountable and coming after Trump on foreign policy issues. The pair were the most consistent Republicans to condemn the White House and advocate for congressional oversight.

Graham would be seen as the lone cantankerous Republican voice in the Senate willing to attack the president's policies and may not be able to assert as much influence.

As chairman of the bipartisan armed services committee, McCain's expertise on national defence and international relations is highly regarded. While the House recently passed the National Defence Authorization Act, McCain's absence could stall debate and movement of the Senate version of the House bill, which would authorize $696 billion in defence spending.

It isn't yet known when McCain might return to Washington. He was reportedly making phone calls about the health-care bill after surgery to remove a blood clot and tumour. Doctors are reviewing treatment options, including chemotherapy and radiation.

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McCain has given no indication he's ready to leave the Senate, tweeting on Thursday: "Unfortunately for my sparring partners in Congress, I'll be back soon, so stand-by!"

While the state election director for Arizona's Secretary of State Eric Spencer was reluctant to count out McCain, who has survived five years as a prisoner of war in Vietnam as well as a previous battle with melanoma and two presidential campaigns in 2000 and 2008, the official acknowledged conversations about the process of finding a replacement are happening in the background.

"Although it's certainly prudent to think about the path of replacement would be, the mantra here is that the senator will fight this and keep on ticking," Spencer said.

If McCain does leave office, under Arizona law, the governor would appoint a replacement from the same party who would not serve out the remainder of the senator's six-year term, but rather until the next regularly scheduled election. That would happen next year.

Political analyst and pollster Ron Faucheux said that whoever assumes the role would have a tough job.

"Given his personal heroism in the Vietnam War, the attention the media gives him, and his outspoken nature, John McCain had a more significant presence in the Senate than most other senators have had," Faucheux said. "It would be impossible for a freshman senator to match that."